Manufactruing thionyl chloride



Dec. 2, 1947.- A. PEcHuKAs MANUFACTURING THIONYL CHLORIDE 2 Sheets-Shed; l

Filed Feb. 16, 1946 Dec. 2, l1947.

A. PECHUKAS MANUFACTURING THIONYL CHLORIDE Filed Feb. 16, 1946 `2 Sheets-Sheet 2 INVENTOR. HL PHO/V55 Pfam/Kms HTTOP/VEK Patented Dec. 2, 1947 UNITED STATES PATENT NO-IF'FICE UFA-CTURING THIONYL CHLORIDE Ailphonse slechukas, Akron, Ohio, assignor to Pittsburgh, Plate `Glass Company, Allegheny County-y, `Pa., acorporation of Pennsylvania Application February 16, 1946, Serial No. 648,152

(Cl. v'Z3-'2031) results in a crude reaction product which -is predominantly thionyl chlor'ideiand in which thevbyproducts and unconverted reactants are such'that they can be easily removed. recovered and reused as additional vcharging stock.

Other objects 'and advantages of the invention will be apparent `-from consideration of the following description of the invention and certain specific embodiments thereof.

Thionyl chloride is a well-known Alaboratory reagent. However, `itsutilization in commercial operations has been restricted because of 'its high cost and lack of large scale production facilities.

The prepa-ration of thionyl chloride by treating `dry sulfur `dioxide with :phosphorous pentachloride is Well-known, but the reaction product 'is contaminated with undesirable phosphorous compounds, the elimination of which 'is attended Vby considerable `fd-iiiiculty and expense. Thionyl chloride is also obtained by the action of chlorine monoxide upon .sulfur at temperatures 'below C. rihis process has not been adopted cornmercially because `it is extremelydiliicult to control and involves the handling lof an explosive :mixture which is easily detonated. In U. S. Patent No. 1 v861,900 there .is disclosed yet another process based on the following reaction conducted in the presence of a mercurio chloride catalyst:

The end products of the reaction Iare `easily separated, .but the process "is uneconomicai because the Icy-products, sulfur `dioxide Aand hydrogen chloride, predominate .and vcan-not be reused in the reaction. As #commercially offered, the thi- 4onyl chloride produced by the foregoing `process is contaminated with sulfuryl chloride.

According to fthe present invention a sulfur chloride `is converted -to'thionyl chloride by reaction with 4suliuradioxicle and chlorine, presumably according to :one :Lof the following equations:

'.Ihe reactants are contacted in the presence of -a catalyst, preferably activated carbon, vand conditions are controlled so that the temperature in the reaction zone is iat Vleast high enough 'to prevent formation -of sulfuryl -chloride (802012).,

Appreciable conversion of the "sulfur chloride takes place at temperatures betwe'en 150 C. and 400 C. Although these temperatures dolnotfdeiine critical limits beyond which no conversion takes place, nevertheless lower or higher temperatures do Ynot Afacilitate significant yield-s. The temperature fis always maintained above 100 C. to prevent iorma'ti'onfofSOClz.

'The reactions involved `are reversible and, ac-

cording'ly, I prefer to adjust the temperature of the reactants while in contact with fthe catalyst mass to a'iordthe presence ofthe maximum possible vamount fof iundissoca'ted thionyl chlorideat the completion .oi the reaction. Where the -reaction zone is maintained at approximately -u-niform temperature throughout, I have discovered that optimum yields are obtained when the temperature of the `Ireaction Azone 1is maintained at about 200 fC.

The reaction zisexothermic. 1n large-scale operations, `Where "the gaseous reactants :are passed through a ycatalyst bed of appreciable cross sec- -`tion, it is convenient to allowthetemperature .to rise considerably iabove 200 C. at :the outset `while controlling the ultimate temperature ofthe reactants before 'leaving `the reaction zone to insure that they are at a temperature of 200 C or below prior to removal and recovery.

The conversion of a sulfur chloride to thionyl chloride in accordance vwith the invention 1 may Vbe conducted-batchwise or continuously.

Under theconditions prevailing .in the .reaction zone, it -is fnot entirely clear which -chloride of sulfur is principally :involved in the reaction with chlorine and SO2. However, this fact is immaterial to the successful practice-of rthe invention. At the temperatures required :to 4obtain fgood yields of thonyl chloride, sulfur, chlorine and two Vchlorides-oi sul-fur Iare all `preset-itin the zone .as indicated by the `eotuili-briurn reactions:

Thus, all that is necessary is for the -S-SOz--Clz proportion 'to 'be balanced-adequately ior efficient `conversion to take place.

I rind it expedient `to :maintain an excess of SO2, C12 `or both i-n the `feed tothe reactor.

inasmuch `as fsulphuryl chloride, -SO2C12, fdis- Vsociates completely ,to lSO2 vand C12 at temperatures over C., one may use SCzClz tosupply part of the requirements. YBy-tl'iesame tok-en, the lower temperature limit of useful ,conversion conditions fis .slightly .above the temperature `(100 C.)

3 at which SO2 and C12 will associate to form SOzClz.

Considerable variation is possible in the manner of introducing the charge so as to bring about contact of the necessary reactants in the presence of the catalyst. For instance, I have charged a liquid mixture of equimolecular amounts of sulfuryl chloride and sulfur dichloride together with an excess of chlorine to a hot catalyst bed maintained at 200 C., and have obtained thionyl chloride in the eilluent from the bed. Yields are low and control of the charge is difficult because of surging upon sudden evaporation of the liquid.

Preferably, the sulfur monochloride or dichloride is preheated and vaporized before introduction to the reactor. This can be facilitated by using chlorine as a vaporization aid, bubbling it through the hot liquid sulfur chloride and passing the emanating vapors to the hot reaction zone.

Regardless of the particular sulfur chloride charged to the reaction zone, the crude reaction product recovered therefrom contains appreciable quantities of both sulfur chlorides in addition to unreacted SO2 and C12. This is inevitable in view of the association of sulfur and chlorine in the system under the conditions prevailing. Hence, a typical crude reaction product resulting from a single pass conversion of sulfur monochloride after removal of unreacted SO2 and C12 may contain something over ilfty per cent thionyl chloride with the balance containing equal proportions of the monoand di-chlorides of sulfur. Again, a similar reaction product may contain a preponderance of one chloride over the other. but there is always an appreciable amount of each.

Ordinarily, the efuent from the reaction zone is conducted through a water cooled condenser and hence to a separator or degasser where SO2 and C12 are removed as gases, leaving a liquid residue which consists practically entirely of thionyl chloride and the monoand di-chlorides of sulfur. The liquid residue is marked by complete freedom from contamination with sulfuryl chloride which distinguishes it from certain other commercial products.

The relative proportion of SO2 and C12 in the oiT gas depends on the feed and the conditions prevailing in the system, but in all events after analysis the mixed gases can be recycled to the feed with suilicient make-up either component to establish the required balance in the feed.

Under some conditions, it is convenient for metering purposes to pass the 01T gases over cold activated charcoal to convert the minor component entirely to sulfuryl chloride, a liquid. Ii desired, the deficiency in the minor component can be augmented by make-up so that the two reactants pass over the cold charcoal in equimolecular proportions and are entirely converted to sulfuryl chloride. In either event, the sulfuryl chloride can be used as such or heated to dissociate it prior to the recycle feed back, inasmuch as the SO2 and C12 content of the liquid is readily determinable.

The liquid residue after removal of SO2 and C12 is topped to remove a fraction containing principally sulfur dichloride which can be recycled to the feed. The bottoms are then distilled in a column under vacuum to separate an overhead fraction containing ninety-five per cent or more thionyl chloride,

Advantageously, after removal of the off gases, the liquid residue from the condenser is subjected to a purification operation involving addition of sulfur and an iron-containing catalyst thereto followed by distillation. This purification operation is a separate invention described and claimed in the co-pending application of Fred C. Trager, Serial No. 648,151 entitled Purication of thionyl chloride, and led concurrently herewith.

As therein described, on addition of ilowers of sulfur and an iron-containing catalyst to the crude liquid reaction product, followed by distillation, the sulfur chlorides which contaminate the thionyl chloride are left behind as sulfur monochloride. In the distillation step, purified thionyl chloride is removed overhead, and recovered as a distillate. Water-white thionyl chloride of over 99.0 per cent purity is obtainable by this method.

Employing the aforesaid purication operation in the practice of the present invention, the bottoms remaining after separation of thionyl chloride can be returned to the feed after chlorination to the desired chlorine-sulfur ratio.

In the accompanying drawings, wherein certain specific embodiments o-f the invention are illustrated in diagrammatic fashion;

Fig. I is a schematic representation of certain laboratory apparatus employed in practicing the invention; and

Fig. II is a flow sheet depicting the relationship of the various steps in the process of the invention and showing certain modifications thereof.

Referring to the drawing and more particularly to Fig. I thereof. a stoppered flask I is suspended in a wax bath 2 heated by a flame or other source of heat 3. An inlet tube 4 projects through the stopper and terminates at a low level in flask I. Outlet 5 projects through the stopper into the flask to a point well above the liquid level therein. Outlet 5 after junction with tube 6 leads into one end of a conventional stoppered U-tube reactor 'I nearly lled with a body of iinely divided activated charcoal 8 and suspended in a wax bath 9, heated as at 3. From the other end of U-tube 1, a conduit I0 leads through a water-jacketed condenser II into a stoppered receiving ilask I2. A conventional column I3, preferably packed with Pyrex glass spirals communicates at its base with flask I2 and serves to trap uncondensed vapors proceeding toward gas take off I4.

In a typical operation, flask I is nearly filled with a body of sulfur monochloride and the wax in bath 2 is heated to a temperature substantially in excess of 59 C., but below the boiling point of sulfur dichloride, say C.' Chlorine gas is then introduced through inlet 4 at such a rate that sulfur dichloride is continuously formed and vaporized in the ilash l. Vapors of S012 together with any excess C12 and some vapors of sulfur monochloride emanating from flask I are removed through outlet 5. Sulfur dioxide and additional chlorine are introduced into the stream via tube 6 and the mixed vapors proceed to the inlet side of U-tube l. 'I'he wax bath S is maintained at a temperature of about 200 C. After passing through hot charcoal bed 8, the reaction products are withdrawn through conduit I0 and subjected to cooling in condenser II from whence the products pass to receiver I2. Chlorides of sulfur and thionyl chloride remain in the flask, unreacted chlorine SO2 being separated and removed as olf gases through outlet I4.

In the following tables there are presented tions in the process modifies; the resultsi.- 5

In these experiments approximately oneethirdi of the chlorine yused was introduced through: the inlet. 4- and the balance, together with the SO2; through tube 6;

6 dissolved very7 slowly and separation oi'44 the thi onyl chloride fraction was di'lcult. Even where no low boiling! fractionl Wasi obtainedv the` thionyl chlordetraction was: highly colored. In certain olf theA experiments catalytic: amounts ot iron were added along` with` sulfur before'y distillationofthe crude thionyl chloride in accordance with the: Trager process described above. In` such'. instances, typiedby lt'xperiments-Nos..24:, 25 andi TABLE-I l Main' Ghargein Gramsl lRaOf'Ghge". Guidev Expire tTimelf Ractif Y Y Gm'Mjm com,

IRun', 111.Tmpfdc, F ath6T E i i 3Recovery,

lamp C- sier, so, i011 l so, c1, @me

130 70-75 250. 140 59 51 l 0. 43j A73 253 120 125 250 1411 54 115 0.53: 1 .es 3513v 125 125 250 i 143 134 244 A 1.07- 1105 352,l 125 200 14e 113 214 1 .07 i105 305 125 150 143 12s 234 1.07' 11.35 210 205 250 140` 100 201 0. 0.93 l 317 205 120 200l 140 102 201 A 0; 0.93m. 340 120 175 1 1719 25 170 0. 53A 0.55 322 230 115 225 149 122 225 0. 53Y 0.93- 34s 205 110 200 135 100 90 0,53 0.44 232l 225 110 200A 135 110 200 0.153 0.39 304 230 110 200 l 135 153 0.07 0.39 359 505 115 200 270 29s 470 0; 53` 10,934 745 255 110 200v f 135 143 fr 0.55 003 202 235 110 200 135 18s 312 0.3'Y 1.33 330 255 110 200 135 204 237 0;s 0.93 351 255 110 200 135 155 240 m59 :0;93 359 335 115 200 135 35s 20s 1;.07 l0.30` 371 250 125 200 135y 27s 231 1.07y 0; 110v 370l 250 125 200 1 135K 20s 231 1 0.13 0:39 354 240 130 x 200 135v 257 213.` `107 re30 351 240 130 225V 135` 277 233 107 '0.00 i 333 250 130 175 f 135 20s 243V 107 '0.00 1 234 205 130 200 135- 240 2 01 117 .0.03 355 215 125 200V 135 252 211 117 0.93 371 245 115 200 135 237 240 117 .0.0511 373 In analysis of the crude liquidr reaction product recovered in receiver l2, a packed column with a distilling head Was employed to control re'ux rates.

TABLE II 26,. the' dichloride wasl almost immediately convetted to monochloridev with evolution of heat'. The SO'Clz4 recovered on distillation Was of. much lighter color than. the fractions obtained in other analyses.

Analyzing the data presented in the tablesrit is evident. that when the catalyst bed is maintained Product Analysis at a temperature below C. or above 225 C..

Y the yield is poor. Best yields were obtained at 131511111151011 Analysis per (ggeld 45 269or C. Y As far. as. determinable from the avail- Exp N able` datafcontact time has little or no effect on B P to v n yields. While ther concentration oithevreactants 721 o., 737-6., C Siggi 2h81; can be varied over wide limits Without appreci- Gmsable effect on yields, the data show that a de- 50 ciency in. chlorine is definitely undesirable. An excess over theoretical amounts of about 100 per 232 101 4514 cent for SO2 and 0- to I0 per cent for C12 appear 22g to be most desirable.` 115 454 In Fig. 2 there is illustrated diagrammatically apreferred embodiment of the invention wherein 201 573 y the process vcan be operated continuously with 12g; l certain optional modifications. In conducting 303 i the process of the invention in accordance with [1S-4L the diagram, sulfur monochloride is Withdrawn 250 540 60 from storage and introduced through line 30 to ggg apreheater A WhereA it is brought to a tempera- 34 7012 ture of approximately 125 C. Chlorine from storage isv introduced through line. 3l into the 320 07'. 2 preheater A where it serves to form. sulfur. di-Y 5v chloride which. is vaporized. and conducted. 312 555 through line 321 toward the main reactor B. Sul-- $829 fur dioxide and chlorine from. storage are introduced into lineA 32 through lines 33 and 34 respectively just before entry into the main reactor The fraction boiling up to '74 C. is principally 70 B. In the main reactor the reactants pass in SC12; that boiling from '24 to 76 C. is principally intimate admixture through a bed of activated thionyl chloride, While the distillation residue is charcoal or carbon. If desired, the bed can be sulfur and sulfur monochloride. maintained at uniform temperature throughout Sulfur was added to the crude liquid before disby means of conventional controls. In such intillation. In the absence of iron the sulfur was 75 stances, high yields are favored by maintaining the bed within a temperature range of 175 to 225 C.

Alternatively, once the reaction is initiated the temperature of the forepart of the bed may be permitted to be controlled only by the heat evolved during the initial part of the reaction, while the afterpart of the bed is so controlled that the eflluent from the main reactor is at a temperature of 200 C. or slightly below whereby undue dissociation of the thionyl chloride formed is prevented.

From the main reactor, the reaction products are removed through line 35 to a water cooled condenser C where all the thionyl chloride is removed as condensate. The crude condensate is removed through line 35 to a Adegasser D where dissolved chlorine and SO2 are removed as vapo-rs and after joining the uncondensed gases removed from the condenser through line 3l they pass to the inlet side of a blower E through conduit 38.

Degassed condensate from the degasser is removed through line 39 to a sulfurizer F where flowers of sulfur are added in amount substam.

tially in excess of that required to convert any SClz to the monochloride together with a catalytic amount of a substance such as FeCls capable of yielding ferric ions. Thence, via line 40 the sulfurized crude product is introduced into a still G where it is heated to remove purified thionyl chloride as an overhead which is condensed and recovered as the main product. The still bottoms, consisting mainly of sulfur monochloride admixed with elemental sulfur are preferably withdrawn through line 4l and passed to a chlor- .i

inater 4 where they are chlorinated to any desired degree prior to being recycled to the charge entering the preheater A. SO2 and chlorine as oil gases from the main reaction may be returned to the charge via lines 42, 34 and 32. Alternatively, the oi gases may be introduced through line 43 into a converter I where, in the presence of cold charcoal, the SO2 and chlorine in the 01T gas (together with such makeup as is necessary to obtain stoichiometric proportions of the two components) combine to form sulfuryl chloride, a liquid. On removal from the converter through line 43 the sulfuryl chloride is readily metered prior to introduction into a vaporizer J where the liquid is vaporized and recycled throughline 45 to the stream entering the main reactor. The alternative treatment of the off gases just described is shown in dotted lines in the drawing.

If desired, the chlorinater H may be omitted from the cycle of operations, sulfur and sulfur monochloride from the still G being recycled directly to the preheater A where additional chlorine is supplied to convert elemental sulfur to the chloride.

Under properly controlled conditions, theconversion of sulfur and chlorine (the principal reactants from the viewpoint of economy) to thionyl chloride is nearly 100 per cent ecient.

What I claim is: g

1. A process which comprises contacting a sulfur chloride with sulfur dioxide and chlorine in the presence of a catalyst at a temperature above 100 C. and recovering a reaction product containing thionyl chloride.

2. A process which comprises contacting a sulfur chloride with sulfur dioxide and chlorine in the presence of activated carbon and recovering a reaction product containing thionyl chloride.

3. A process which comprises forming a vapor phase mixture of sulfur dichloride, sulfur dioxide and chlorine, passing the mixture through a hot bed of activated carbon, cooling the effluent vapors to separate a liquid fraction containingY chlorine to form a gaseous stream of charging stock, passing said stream through a hot bed of activated carbon to generate thionyl chloride, removing the gaseous reaction products, condensving therefrom a liquid fraction containing thionyl chloride, separating such fraction, removing uncondensed gases as an overhead and recycling such overhead to said stream of charging stock.

5. A process which comprises vaporizing a chloride of sulfur, admixing therewith sulfur dioxide and chlorine each in excess of the stoichiometric amount required to form thionyl chloride, passing the mixed vapors through a bed of hot activated carbon, controlling the temperature of the bed so that the vapors emerge therefrom at a temperature of approximately 200 C., cooling the effluent from the bed to separate therefrom a liquid fraction containing thionyl chloride and recovering the liquid fraction so formed.

6. A continuous process of manufacturing thionyl chloride which comprises maintaining a body of sulfur monochloride at a temperature substantially in excess of 59 C. but below the boiling point of sulfur monochloride, continuously introducing chlorine gas into said body together with additional sulfur monochloride, continuously removing vapors of sulfur dichloride so formed and bringing them into admixture with gaseous chlorine and sulfur dioxide, passing the mixture through a hot bed of activated carbon under conditions so controlled that the temperature of the eiliuent from the bed is between C. and 225 C., subjecting the gases after passage through the bed to condensation to separate out a liquid fraction containing thionyl chloride and sulfur chloride, removing unreacted sulfur dioxide and chlorine as an overhead and directing said overhead through a bed of cold activated carbon to form sulfuryl chloride, vaporizing said sulfuryl chloride, recycling said vapors to the mixture passing to the hot carbon bed, distilling said liquid fraction containing thionyl chloride in the presence of an excess of elemental sulfur to separate and recover puried thionyl chloride as a distillate, continuously withdrawing still bottoms containing sulfur monochloride and sulfur,

subjecting said still bottoms to chlorination to.

form sulfur chloride and recycling said sulfur chloride to the feed.

ALPHONSE PECHUKAS. 

